1. Field of the Invention
The present invention relates to a spring spacer for use with a spring of a suspension system for a vehicle. Preferably, the spring is made of a material such as Ti or the like, and has a low surface hardness.
2. Description of the Related Art
In recent years, motorcycles used for specific applications such as racing or the like utilize springs made of Titanium (Ti). Springs made of Ti are lightweight as compared to conventional springs made of Iron (Fe). For example, a suspension unit that has a Ti spring may weigh 200 to 500 g (by spring constant) less than a suspension unit that utilizes a conventional spring made of Fe.
While Ti springs are advantageously lightweight, they are prone to wear and have a lower durability due to their low surface hardness. Ti springs may have a hardness as low as Ti:Hv420 as compared with Fe:Hv550. Due to their low durability, Ti springs are often replaced after 1 or 2 races of a motorcycle.
In addition, Ti valve springs are utilized for engine intake and exhaust valves of vehicles. Since such Ti valve springs rapidly expand and contract at high speed, some valve springs are used with means to prevent contact and abrasion between a first turn and a second turn of the spring. For example, U.S. Pat. Specification No. 4,993,376 proposes a spring unit, in which an end of a first turn of a Ti valve spring is insert-molded in a spring seat made of a synthetic resin in order to prevent abutment between the end of the first turn of the valve spring and the second turn.
The spring seats are cylindrically-shaped and have an annular flange integrally molded to one end edge. Spring seats are fitted onto both ends of the valve spring. One of the spring seats abuts against a spring retainer and is held by a spring bearing surface (indicates a surface that bears a load of the spring) of the spring retainer. The other spring seat abuts a cylinder head and is held by a spring bearing surface or annular flat surface on the cylinder head, through a washer-shaped spring seat.
With such construction, the end of the first turn of the valve spring is insert-molded in the spring seat made of a synthetic resin. Abutment between the end of the first turn of the valve spring and the second turn is prevented, which prevents contact abrasion of the second turn.
Also, another disclosed embodiment of the spring unit has a shoulder surface comprising a circumferentially inclined surface bearing an end of the valve spring is provided on the spring seat and is made integral therewith. With such construction, the shoulder surface is interposed between the end of the first turn and the second turn of the valve spring to prevent contact abrasion of the second turn.
While the spring seat is intended for a valve spring unit of an internal combustion engine, the spring seat may also be utilized in a unit, such as a vehicular suspension unit having a large spring. A suspension spring having a large diameter wire involves a larger individual dispersion at both spring ends as compared with the valve spring. Therefore, there is a need for clearance to accommodate the individual dispersion between the shoulder surface and the second turn by lowering the shoulder surface interposed between an end of a first turn and a second turn of the suspension spring.
However, the clearance may permit the spring seat to rotate during assembly of the suspension unit and cause movement of the shoulder surface relative to the suspension spring. This relative movement may allow contact between the first and second turns of the spring.
A worker may deliberately prevent this rotation of the spring seat at the time of assembling the suspension unit. However, this additional step may decrease productivity.
Also, in this case, several kinds of spring seats may be formed with shoulder surfaces of different heights. The spring seats are selectively matched and assembled with springs taken into account each springs dispersion. However, this matching process of temporarily mounting the different height spring seats with each spring and selecting an optimum spring seat for the spring may decrease productivity.
On the other hand, in the case where an end of a first turn of a suspension spring is insert-molded in a spring seat made of a synthetic resin, the problem described above is overcome but the molding process of the spring seat in a large-sized suspension spring is complex and may decrease productivity.